A subsurface safety valve (SSV) is one commonly used type of down-hole valve which is controlled between a fully open or fully closed position by control lines extending from the valve, usually mounted in a tubing string to the surface.
Other applications require control of the flow as opposed to the on/off capabilities of an SSV. A particular example of this is in the application of a downhole oil/water separator where the valve is used to control the injection rate of the water back into the formation. Since formations change injectivity or resistance to injection of fluid over time, one way to maintain a near-constant backpressure on the separator is to adjust the outlet flow rate of separated water back to the formation. The apparatus of the present invention facilitates this procedure by providing infinite adjustability between a max and minimum flow for a given upstream pressure in the separator.
In the past, auxiliary controlled valves have been used in drillstrings as a signal source for transmitting information from the well to the surface where flushing fluid flows through the string and serves as the transmitting medium. Such a valve is illustrated in U.S. Pat. No. 4,519,574. This valve relies on down-hole differential pressures coupled with an auxiliary power source to operate a solenoid to control an associated hydraulic circuit for positioning the valve member in one of two extreme positions.
It is the object of the present invention to provide a simple valve design which allows throttling with control from the surface via a control line or another signaling technique. Another objective of one embodiment of the present invention is to allow a minimum flow, via a central opening, so that tools can be passed through the valve while it is in its minimum flow or maximum throttling position. Another objective of the present invention is to provide improved control for downhole operations where sensitivity is required to changing conditions which requires regulation of applied pressures in fluids being delivered downhole. Those and other advantages of the invention will become more apparent from a detailed description of the preferred embodiment which appears below.